Touch screen devices (mobile phones, tablets, netbooks, even personal computers) are becoming more and more popular. But if you decide to buy a device whose screen responds to touch, you should know that there are different touch screen types.
Different types of touch screens work on different physical principles.. There are two main types of touch screens - capacitive and resistive. There are other types, for example, screens on surface acoustic waves, infrared, optical, strain gauge, induction (used in), etc. But the chance to encounter these types of screens in everyday life is quite small, so let's talk about the two most common types of touchscreens .
Touch screen types: resistive
Resistive touch screen is a simpler and cheaper technology. Such a screen consists of two main parts: a conductive substrate and a plastic membrane. When you press the membrane, it closes with the substrate. In this case, the control electronics calculates the resistance that occurs between the edges of the membrane and the substrate, and thus determines the coordinates of the pressure point.
Resistive touch screens are used in PDAs, communicators, some models of mobile phones, POS-terminals, tablet computers, industrial control devices, medical equipment. Usually, small-sized devices equipped with a resistive screen are equipped with a stylus to make it more convenient to press the membrane (with a small screen area, it is difficult to do this with a finger).
A significant advantage of resistive screens is their simplicity and low cost., which ultimately reduces the price of the entire device. They are also stain resistant. But the main thing is that even in the absence of a special stylus, you can work with them with almost any hard, blunt object that is at hand. They also react to the touch of fingers, even if the hand is in a glove, however, the touch should be strong enough.
But resistive screens also have their drawbacks.. This type of touch screen is sensitive to mechanical damage: if you use an inappropriate object instead of a stylus or, say, store your phone in the same pocket as your keys, you can easily scratch it. Therefore, for devices with this type of screens, it is better to additionally purchase a special protective film. The sensitivity of resistive screens decreases at low temperatures. In addition, their transparency also leaves much to be desired: they transmit a maximum of 85% of the light coming from the display.
Touch screen types: capacitive
Capacitive touch screens take advantage of the fact that high-capacity objects (in this case, a person) conduct alternating electrical current. Such screens are a panel of glass, which is covered with a transparent resistive alloy. A small alternating voltage is transmitted to the conductive layer. If you touch your finger with a screen or other conductive object, current leakage occurs, it is detected by sensors, and the coordinates of the point of pressing are calculated.
There are conventional capacitive screens and projective-capacitive. The second technology is more "advanced". Such screens are more sensitive (say, they react to a gloved hand, depending on just capacitive ones), support multi-touch technology(simultaneous determination of the coordinates of several touch points). Capacitive screens are used in ATMs, information kiosks and protected areas. Projection-capacitive - in outdoor electronic kiosks, payment terminals, ATMs, laptop touchpads, smartphones and other devices that support multi-touch technology.
Advantages of such touch screens- this is durability, resistance to most contaminants (to those that do not conduct current), high transparency of the screen, the ability to work at low temperatures. If necessary, high strength can be ensured - a glass layer on a capacitive screen can be up to 2 cm thick. Capacitive screens respond to the slightest touch. Projected capacitive screens also support multi-touch.
The disadvantage of capacitive screens is a higher cost compared to resistive ones.. In addition, such screens only respond to conductive objects: a finger or a special stylus (not the same as used with resistive screens). Some craftsmen manage to use sausages, but where is the guarantee that the sausage will be at hand at the right time?
As you can see Different types of touch screens have their own advantages and disadvantages., so it's up to you to decide which one is more suitable for you personally.
In our time, touch screens have long ceased to be exotic. They all look similar on the outside, but are these displays really the same? Let's look at the design of the main types of sensitive screens, their advantages, disadvantages and scope.
Today, sensors based on capacitive and resistive technologies, as well as their varieties, are most widely used.
"Multitouch"
This is the name of the technology that allows you to recognize pressing the touch screen at several points at the same time. This opens up new possibilities in device management. An example of the use of multi-touch technology is the Apple iPhone interface.
Capacitive touch screens
 | For example: Tne Prada Phoneby LG |
The capacitive touch display actually responds to touch. It is a glass panel coated with a transparent conductive compound. Four electrodes are placed at the corners of the panel, to which an alternating current is supplied. At the moment when the user touches such a screen with a finger, an electric charge from the conductive layer flows through the skin to the human body. The screen controller measures the strength of the resulting current through all four electrodes - it is proportional to the distance from the corner of the panel to the point of contact. Comparing the obtained values, you can find out the exact coordinates of the touch point. Sensors operating on this principle can be distinguished “by touch” - they are triggered by a light touch, and they respond faster and more clearly to pressing with a fingertip than with a fingernail. Moreover, they do not respond to pressing by any other objects, especially if they are non-conductive. Therefore, a phone with such a screen cannot be operated with a gloved hand. In addition, as the temperature drops, the electrical characteristics of the sensor change, and the screen starts to work worse. We add that this principle is usually used in laptop touchpads.
 |
|
 | For example: Apple iPhone |
Projected capacitive screens
There is another type of capacitive sensor - projected-capacitive screen. On the back side of it is a grid of electrodes. At the place where the hand touches, the electrical capacitance changes (according to the laws of electrodynamics, the human body is a capacitor), the controller determines at which intersection of the electrodes this happened, and calculates the coordinates. Such screens, in addition to high transparency and durability, have two more important advantages - the glass substrate can be made arbitrarily strong (and rather thick), besides, they support "multi-touch". Minus - lower accuracy compared to conventional capacitive technology.
Resistive touch screens
 |
|
 | For example: HTC Touch Diamond |
The resistive sensor de facto responds to pressure. The screen consists of two plates, between which there is a composition that does not conduct electric current. If you touch the outer flexible (and transparent) plate with your finger (or any other object - in this case it does not matter), the plates close and current begins to flow at the point of contact. To determine the place of touch, the screen controller measures the voltage in pairs between the electrodes placed at the edges of the panel. Such a screen is called a 4-wire screen (there are also 5-wire ones, which have some differences).
The peculiarity of the resistive screen is that it requires physical effort to operate, and it recognizes pressing with a fingernail better than with a small pad, and reacts to any objects touching the surface. Devices with resistive screens are often equipped with styluses. Such a display provides higher control accuracy (with a stylus it is really possible to literally hit a pixel, while a finger on a capacitive screen can only hit a fairly large area), but due to constant contact with solid objects, the flexible plate is quickly covered with scratches. Most mobile devices are equipped with resistive screens.
Other types of touch screens
There are a number of sensor technologies, often quite exotic. For example, using a grid of infrared rays or even generating ultrasonic vibrations. The latter is known as surface acoustic wave technology. There are systems based on cameras that track movement (multi-touch is also supported here), and based on tenso-coatings, the deformation of which changes the electrical resistance.
The touch display, as an input-output device of information, appeared relatively long ago. Back in the 90s of the last century, PDAs and other portable devices equipped with a touchscreen could be found on sale. As technology has evolved, touchscreen smartphones have improved and new requirements have been put forward, so touchscreens have changed dramatically over the past decade.
Resistive sensors
The simplest and most affordable sensors for smartphones. They consist of two layers, on which a grid of transparent conductive material is applied. The lower one is made of glass (mineral or organic), and the upper one is made of plastic. Between them is a thin air layer. At the moment of touching, the circuit is closed between the grids of different layers, and the controller determines the coordinates of the place of pressing.
The advantages of resistive screens are sensitivity to pressing any object, low cost, simplicity of design and accuracy. The main drawback is fragility: the plastic top layer is easy to cut or pierce, after which the contact will be broken and the sensor will not work.
Resistive sensors also have relatively low transparency (up to 80%), therefore, starting from 2010, they are becoming obsolete on smartphones. Today, such a touchscreen can only be found in cheap Chinese-made phones.
Capacitive sensors
Smartphone capacitive sensors consist of a glass panel covered with a transparent conductive layer and four corner sensors. A weak alternating current is supplied to it, the leakage of which, when touched, is recorded by sensors, calculating the coordinates of pressing. In addition to the fact that such touchscreens react only to touching an object with electrical conductivity, they have low accuracy and are not able to simultaneously perceive several clicks.
Capacitive projection sensors
The most common type of sensors on modern smartphones. They are a development of the previous type. Instead of a conductive layer, a grid of electrodes is applied to the panel, which are also energized. At the moment of touching the finger, acting as a capacitor, a current leakage occurs, the location of which is calculated by the controller. This design makes it possible to track several touches (currently up to 10, more - it does not make sense) at the same time.
The fundamental design of such touchscreens is being modified by mobile device manufacturers. On modern OGS smartphone displays, sensitive electrodes can be mounted directly between the crystals (or diodes) of the matrix, and for resistance to damage, the screen is covered with tempered glass.
Previously, it was also practiced to separate the protective glass and the sensor layer: the electrodes were applied to a transparent film, which was covered with glass on top. This approach made it possible to maintain the sensor's performance even in the presence of serious damage (cracks, chips).
Great post from omgadget.ru on how touch screens work. I have long wanted to know why iPhones can be controlled with a finger, but not with a pencil, for example.
Today's touch screens are divided into several types depending on the physical principle of operation: resistive (four-, five- or eight-wire), capacitive, projected-capacitive, matrix, surface-acoustic wave screens, optical, strain gauge and screens based on infrared rays .
There are even more patented technology names - several dozen. The most widespread are resistive and capacitive screens, while the rest are either hopelessly outdated or highly specialized.
Resistive screen
The simplest type of resistive screen to implement is a four-wire one. It consists of a glass panel and a flexible plastic membrane coated with a thin conductive coating. The space between the glass and the membrane is filled with micro-insulators, which reliably insulate conductive surfaces. Along the edges of each layer are thin metal plates - electrodes. In the back layer with resistive material they are located vertically, and in the front layer they are horizontal, which is necessary for calculating the coordinates. When the screen is pressed, the panel and the membrane are closed, a special sensor registers the change in resistance at the point of pressing and converts it into a signal. An improved variation are eight-wire touch screens. Their accuracy is higher, but reliability and durability are lame.
The five-wire screen is more reliable due to the fact that the resistive coating on the membrane is replaced by a conductive one, which will continue to work even with a damaged membrane. The rear glass is coated with four electrodes at the corners that are constantly energized. But the fifth electrode is the output of the front conductive layer. As soon as you touch the screen, the upper and lower layers will close, and the controller will first record the change in voltage on the front layer, that is, the very fact of touching. Then, first, two electrodes are grounded horizontally on the back layer, and then two others, but vertically.
LG Optimus GT 540
Capacitive touch screens
A capacitive (like a surface capacitive) screen is more complex and uses the fact that the human body and the screen form a capacitor that conducts alternating current.Such a screen is a glass panel coated with a transparent resistive material to provide electrical contact with the body. Electrodes located at the corners of the screen apply a small alternating voltage to the conductive layer. When touching the screen with a finger or other conductive object, an alternating current leaks through said capacitor. The closer the finger is to the electrode, the lower the resistance of the screen, which means that the current strength is greater. All this is registered by sensors that transmit information for further processing to the processor.
Capacitive touch screens are durable and can withstand up to 200 million clicks. Their accuracy is slightly better than resistive ones, and transparency exceeds 90%. However, such displays are afraid of liquids, non-conductive pollution.
iPhone3G
Matrix touch screens
Here the design is very reminiscent of a resistive screen, but simplified to disgrace. Horizontal conductors are applied to the glass, vertical conductors are applied to the membrane. When the screen is touched, the conductors touch and close crosswise.The processor keeps track of which conductors are closed, and then easily calculates the coordinates of pressing. That's actually all. Such screens have very low accuracy compared to other types of touchscreens, so they have not been used for a long time. A matrix panel can also be just a panel of buttons located at the crosshairs of the conductors.
Projected capacitive touch screens
But projected capacitive displays support simultaneous pressing in several places, although they have an even more complex structure. On the inner side of such a screen, a grid of electrodes is applied, upon contact with which a capacitor is formed. In the place where the capacitor is formed, its electric capacitance changes, and the controller determines the point of intersection of the electrodes. Then everything is as usual - the controller, calculations, coordinates.
If you touch the screen in different places, then several capacitors are formed, which makes it possible to implement multi-touch technology.
iPad 2
Infrared grid screen
The principle of operation of the infrared touch panel is simple and somewhat reminiscent of a matrix.Only here the vertical and horizontal conductors are replaced by infrared rays. Around such a display is a frame with built-in emitters and receivers. At the moment such a display is touched, some rays overlap and do not reach their destination - the receiver. Further, the controller will not be difficult to calculate the place of contact.
Such displays perfectly transmit light and are extremely durable, because they do without a sensitive coating at all. However, they do not have the highest accuracy and are afraid of pollution. Huge bezels up to 150 inches are now available for use in conjunction with a projector or regular monitor.
Sony Reader PRS-650
Touch screens based on surface acoustic waves (SAW)
This screen with a frightening name is a glass panel with piezoelectric transducers (PETs) built into the corners. Along the perimeter of the display are reflective and receiving sensors. The controller generates high frequency signals and sends it to the PET. That, in turn, converts this signal into acoustic vibrations, which are reflected from reflective sensors. The reflected waves are then picked up by receivers and sent back to the PET to be converted back into an electrical signal. When you touch the screen with your finger, part of the energy of the acoustic waves is absorbed. Receivers pick up this change, and a complex processor calculates the position of the touch point.The main advantage of the SAW screen is the ability to track not only the coordinates of the point, but also the force of pressing, due to the fact that the degree of absorption of acoustic waves depends on the pressure at the point of contact. This device has a very high transparency, since the display of the image from the screen occurs without any obstacles in the form of conductive layers, as is done in resistive screens. Such screens are difficult to implement, but quite durable. They can withstand up to 50 million touches and are often used in arcade machines, secure help systems and educational institutions. The main disadvantage of the screen on SAW are failures in the presence of vibration and noise, as well as when the screen is dirty.
Almost the whole world of high technologies has already been captured by the fashion for touch displays. Now almost every player or cell phone has a touchscreen, and the general scope of such display technology is much more significant. There are different types of touch screens on the market today, depending on the technology they use.
It is a device focused on the input and output of information through a touch-sensitive display. On the screens of modern devices, not only images are shown, but there are also opportunities to interact with them. Initially, such a connection was provided through the buttons familiar to all, then a different type of manipulator appeared, called a mouse, which greatly facilitated the process. This device requires a horizontal surface to operate, which is quite inconvenient when using a mobile phone. This is where the addition to the usual screen in the form of a touchscreen came in handy. The touch element is not inherently a screen, it is an additional device that is placed outside on top of the display, while it protects and is designed to enter coordinates by touching it with an input device or a finger. There are different types of touch screens. It is worth considering them in a little more detail.
Types of touch screens and their use in electronic devices
Initially, touchscreen technology was used for handheld computers, but at the moment it has received a much wider use, from players to cameras. Since such a control mechanism is very convenient, it is used for modern ATMs, tablet terminals, various electronic directories and other devices. Touch screen technology is very useful in cases where you need instant access to the controlled device without any preparation and with maximum interactivity: the controls change depending on which function is activated.
Types of touch screens: capacitive, resistive, projected-capacitive and others (less popular). In addition to these types, there are also infrared and matrix displays, but their accuracy is so low that their scope is quite limited.
Resistive touch screens
These displays are the simplest devices. Such a panel includes a conductive substrate and a plastic membrane, which have a certain resistance. When the membrane is pressed, a short circuit is made with the substrate, which forces the conductive electronics to respond to the resistance that has arisen between the edges of these elements, then calculating the coordinates of the point that was pressed. Such screens are very simple, they are cheap, and they also have excellent resistance to pollution. The main advantage of this type of sensor is that it is sensitive to any touch. The disadvantage lies in the high sensitivity to mechanical damage, which requires the use of a special panel. Such panels work great at low temperatures.
Capacitive sensor technology works quite differently. It is based on the principle that a large-capacity object can conduct electric current. An electrically conductive layer is applied to the glass, and an alternating voltage is applied to all four corners. When touching the screen with a grounded object of greater power, current leakage occurs. The control electronics registers these leaks by determining the coordinates.
This article briefly and clearly describes the main types of touch screens that have received the greatest popularity.
